In a time division multiple access system, inbound 102 slot assignments can be requested from a subscriber unit to an infrastructure through a Slot Reservation Request message on either a Random Access slot or a Reserved Access slot. The infrastructure responds on outbound 100 timeslots with a Slot Reservation Request Feedback message 104. It should be noted that the outbound channel is defined as conveying the information flow from the infrastructure to the subscriber units; likewise, the inbound channel is defined as conveying the information flow from the subscriber units to the infrastructure. As shown in FIG. 1 the Feedback message 104 contains the subscriber address 106, the Forward Slot Assignment (SA) field 108 that gives an indication of upcoming slots assigned to the subscriber, and the Slot Type Field (SLT) 110 that indicates if the slot is for random or reserved access. The subscriber transmits blocks on the assigned timeslots as shown in FIG. 1.
The problem with the access scheme is that the Slot Assignment field is limited to seven SA bits. Consequently the assignment can be made only for the next seven slots maximum. After this time a new assignment has to be made. Considering the number of subscribers at the radio sites, and the number of assignment requests being made, the Slot Reservation Request Feedback messages have to be sent very frequently, leaving less bandwidth for data transmissions.
As an example, FIG. 1 shows the outbound timeslot 1 (Slot 1) containing a subscriber assignment identifier that specifies the slot assignment of inbound timeslot 1 (S1).
For a full duplex subscriber unit, all inbound slot assignments made on the outbound channel can be decoded even when transmitting on an inbound timeslot. A half duplex subscriber unit, however, cannot receive the outbound slot assignments made on outbound timeslots that are adjacent to the one it is transmitting inbound as shown in FIG. 1; the half duplex subscriber unit cannot fully utilize the inbound channel. In FIG. 1, a half duplex subscriber unit transmitting on inbound timeslot 7 (Slot 7) cannot receive the slot assignments in the outbound timeslots 8 and 9 (Slot 8 and Slot 9). Slot assignments, containing the slot type field, to the half duplex subscriber unit transmitting in timeslot 7, made in the outbound timeslots 8 and 9 will be missed, resulting in their corresponding inbound timeslots going unused; those outbound timeslots cannot contain data, including slot assignments for the transmitting half duplex subscriber unit. A problem with this method is that a half duplex subscriber unit can only use one in every three inbound timeslots, thus cutting the available throughput by two thirds.
Thus, there exists a need for a method that specifies the resource allocation and access for up to the next N timeslots.